1. Field of the Invention
The present invention relates to polyester compositions and more particularly relates to blow moldable polyester compositions.
2. Description of Related Art
High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described, inter alia, in Whinfield et al., U.S. Pat. No. 2,465,319 and in Pengilly, U.S. Pat. No. 3,047,539.
Such polyesters, however, generally lack the level of melt viscosity and melt strength necessary for many blow molding applications.
Alkali metal salts of an aliphatic polycarboxylic acid containing at least 20 carbon atoms and having a molecular weight of less than about 1500 have been added to copolyester elastomers to produce blow moldable compositions having increased melt strength (See Hoeschele, U.S. Pat. No. 4,362,836.) Sodium salts of polycarboxylic acids containing up to 20 carbon atoms have been added to linear saturated polyesters as nucleating agents (See Herwig et al., U.S. Pat. No. 3,761,450.).
Triazine ring-containing epoxy compounds (e.g., triglycidyl isocyanurate or N-methyl-N,N"-diglycidyl isocyanurate) have been added to fiber reinforced polyethyleneterephthalate (PET) compositions (see JP No. 53/143449 (76.12.14)); polyfunctional compounds (e.g., polyepoxy compounds, polyisocyanate compounds, epoxysilane compounds and aminosilane compounds) have been added to glass fiber reinforced polybutylene terephthalate or polypropylene terephthalate compositions (See JP No. 53/106750 (78.09/18)); and polyfunctional compounds (e.g., polyepoxy compounds, polyisocyanate compounds, epoxy silane compounds, and aminosilane compounds) have been added to glass fiber reinforced polyester resin compositions (See JP No. 53/106749 (78.09.18)).
It has been discovered, however, that using in a polyester composition high levels of salt of a polycarboxylic acid alone can result in the composition exhibiting generally poor levels of impact strength, and using reasonable levels of the multifunctional epoxide alone does not sufficiently reduce the melt flow index.
Accordingly, one object of the present invention is to provide a blow moldable polyester composition exhibiting an enhanced melt viscosity while retaining good levels of impact strength.